Purpose.:
To investigate the prevalence and characteristics of primary angle-closure suspect (PACS), primary angle closure (PAC), and primary angle-closure glaucoma (PACG) in a rural population in China.

Methods.:
In all, 6716 Han Chinese 30 years of age and older (5480 subjects 40 years of age and older) from 13 villages in Handan were randomly selected and completed an ophthalmologic examination, including visual acuity, intraocular pressure (IOP), slit-lamp examination, gonioscopy and stereoscopic photography, and visual field. PACS was defined as present if either eye had the posterior trabecular meshwork not visible for 180° or more on gonioscopy. PAC was present in an eye with PACS and peripheral anterior synechiae (PAS) and/or IOP ≥ 21 mm Hg, but without glaucomatous neuropathy (GON). PACG was defined as PAC with evidence of GON.

Results.:
The standardized prevalences of PACG, PAC, and PACS were 0.5% (95% confidence interval [CI]: 0.3–0.7%), 1.5% (95% CI: 1.2–1.8%), and 10.4% (95% CI: 9.6–11.2%) in those 40 years of age and older. The prevalence of all three conditions increased with age (P < 0.001). Females had much higher rates of PACS, PAC, and PACG (P < 0.05); 21 persons with PACG (65%) were blind in at least one eye: 13 were due to glaucoma and the other 8 likely had other causes.

Conclusions.:
The prevalence of PACS, PAC, and PACG in this rural population is similar to what was previously reported in urban Chinese residents. Two thirds of those with PACG were blind in at least one eye. Strategies to detect and treat this preventable disease in rural China are needed.

Glaucoma is the second leading cause of blindness in the world, and it is estimated that China has half the world's cases of primary angle-closure glaucoma (PACG).1 However, data on PACG prevalence among those living in rural regions of China are lacking, and estimates of the prevalence of PACG for rural China have been based on data from other populations such as those living in Mongolia.2

Early reports using definitions that include intraocular pressure (IOP) and symptoms in the definition of glaucoma reported a prevalence of PACG between 1.4% and 1.6% in Beijing Shunyi County.3,4 In 1995, a study carried out in rural Doumen County in southern China (using a protocol similar to that from Beijing Shunyi County) found a prevalence of 0.64% for PACG subjects older than 45 years of age and 0.85% for subjects older than 50 years of age.5 A separate study from Beijing (2004) reported that PACG was more common among residents living in the suburbs of Beijing than that among those living in the city itself (1.6% vs. 1.1%).6

However, the definitions used in these earlier studies are no longer accepted and the reported rates may not be accurate and comparable.7–9 In 2006, using standardized definitions of glaucoma that do not include IOP in the definition and require optic nerve damage, He et al.10 reported a rate of 2.4% for primary angle closure (PAC, including PACG) and 1.5% for PACG among people 50 years of age and older in urban residents in Guangzhou in south China.

The burden of PACG in rural China, where 650 million persons live, is largely unknown. To improve our understanding of the burden of eye diseases in China, we conducted the Handan Eye Study (HES).11 This study specifically addresses the age- and sex-specific prevalence of primary angle-closure suspect (PACS), PAC, and PACG in a rural population in northern China.

Methods

Study Design

The study population consisted of self-identified Han Chinese, 30 years of age or older, living in rural Handan County, China. Details of the study design, sampling plan, and baseline data were reported elsewhere.11,12 In brief, the study adhered to the Declaration of Helsinki and ethics approval was obtained from the Beijing Tongren Hospital Ethical Committee; written informed consent was obtained from all participants. Residents of Yongnian County, Handan, Hebei province, 30 years of age or older, were randomly selected using a clustered sampling technique, with probabilities proportionate to the size of population in each cluster. In Yongnian County, farmers constitute 90% of the population and Han make up 98% (Han ethnicity accounts for approximately 90% of the Chinese people). Per capita annual net income in this rural area is 3468 Yuan (510$), which was similar to the average income (3255 Yuan, 478$) of those living in rural areas throughout Mainland China.13

Clinical Data

All eligible individuals were invited and scheduled for a detailed eye examination and questionnaire interview, which were performed in a standardized manner at the HES centralized clinic (located in the Yongnian County Hospital). For those subjects who did not present for a complete examination at the central clinic we offered an abbreviated examination carried out in the local village. These examinations included visual acuity, autorefraction, and subjective refraction; questionnaires (the first two villages in which we used an abbreviated form), anterior segment examination with a slit lamp; blood pressure, height, weight, waist/hip ratio, IOP, gonioscopy, and dilated examination and photography (field 1 and field 2) of the fundus. We also obtained sequential stereoscopic optic nerve photographs.

The limbal anterior chamber depth (LACD) was graded as a percentage fraction of the thickness of the adjacent cornea in the following seven categories: 0%, 5%, 15%, 25%, 40%, 75%, and ≥100% referenced on the standard photos.15 Two examiners were involved in grading LACD; the intraclass correlation coefficient (ICC) values were from 0.75 to 0.87. For vertical cup-to-disc ratio (VCDR), 90% of the subjects were examined by one ophthalmologist and the other 10% of subjects were graded by another doctor; the ICC between the examiners was 0.95. Gonioscopy was performed on one in ten participants as well as on all persons with LACD ≤ 40%, IOP > 21 mm Hg, and those having a history of glaucoma, with a gonioscopic lens (Goldmann Magna View; Ocular Instruments, Bellevue, WA) at ×25 magnifications with low ambient illumination. The ophthalmologist performing gonioscopy (GLX) was trained and standardized with a glaucoma expert with experience in angle closure research (DSF and MGH). A narrow vertical beam 1 mm in length was offset vertically for superior and inferior quadrants and horizontally for nasal and temporal quadrants. Small movements of the lens were allowed to visualize the drainage angle, but large movement was avoided because of the possibility of indentation. Dynamic examination with the gonioscopic lens (Goldmann) was performed after static gonioscopy of four quadrants was completed. If a satisfactory examination could not be achieved with the gonioscope (Goldmann lens), a handheld four-mirror gonioscopic lens (Sussman lens; Ocular Instruments) was used. The Spaeth grading system was used to record the results.16

Optic Nerve Evaluation

The optic disc was evaluated using a 78D or 90D lens at ×16 magnification after pupil dilation. The VCDR was used as the key index of structural glaucomatous change. Measurement of VCDR excluded peripapillary atrophy and the scleral ring of Elschnig. The margins of the cup were defined by stereoscopic view as the point of maximum inflection of the vessels crossing the neuroretinal rim. Standard photographs for VCDR from 0.1 to 1.0 in 0.1 increments were used in the grading process.10 Although the final diagnosis was based on fundus photographs of the optic nerve, clinical examination of the optic nerve head was one factor used to determine whether a subject was a “glaucoma suspect” and required additional testing (including gonioscopy and visual field testing). Those with any of the following conditions were identified as glaucoma suspects: IOP > 21 mm Hg, cup/disc ratio ≥ 0.6 (95th percentile of the Handan Eye Study population), cup/disc ratio asymmetry of ≥0.2, optic disc hemorrhage, or a visible retinal nerve fiber layer defect. All glaucoma suspects were requested to come to the central clinic from August 2007 to October 2007 for a definitive examination including visual field testing and gonioscopy.

Visual Field Evaluation

Every 10th person examined as part of the HES was systematically sampled to undergo a visual field test using the standard 24-2 Swedish Interactive Testing Algorithm (SITA) fast program with a visual field analyzer (Humphrey Visual Field Analyzer 750i; Carl Zeiss, Jena, Germany). In addition, all with angle closure or suspect glaucoma had SITA standard visual field tests. Tests were repeated 20 minutes later if the glaucoma hemifield test was outside normal limits, borderline, or if the test was unreliable (i.e., fixation losses > 20%, false positives > 33%, or false negatives > 33%). A visual field compatible with glaucoma was defined as a glaucoma hemifield test result outside normal limits combined with a cluster of four or more contiguous points on the pattern deviation plot (P < 5%) not crossing the horizontal meridian.10,17,18

Glaucoma Diagnosis

Glaucoma suspects had their stereoscopic optic disc photographs evaluated by three glaucoma specialists (LYB, JYQ, and YTC). The photographs were assessed using a stereoscopic viewer (Screen-Vu Stereoscope; PS Manufacturing, Portland, OR). The optic discs were categorized as “definite glaucoma,” “probable glaucoma,” “possible glaucoma,” and “not glaucoma.” These categories were based on the experts' judgment of the probability: definite: to be glaucoma with probability of 90–100%; probable: 70–89%; possible: 30–69%; not glaucoma: <30%. Based on these results, those found to have “definite glaucoma,” “probable glaucoma,” or “possible glaucoma” by any of them were presented to the three senior glaucoma specialists group from China (WNL, RZQ, and LMY) to review and were classified as having definite, probable, possible, or no glaucoma based on consensus using optic nerve head photos, visual fields, and other clinical information.

A second and independent review of the findings was carried out by a glaucoma specialist (DSF) who also classified the patients according to the same definitions. Where the two classifications differed, a final independent adjudication was carried out by another glaucoma specialist (HDJ) and this final assignment was used to determine who had glaucoma. Glaucoma was also diagnosed as present in cases where the optic nerve was not visible due to media opacity and the visual acuity was <20/400 and the IOP was >99.5th percentile, or the visual acuity was <20/400 and the eye had evidence of prior glaucoma filtering surgery, or medical records were available confirming glaucomatous visual morbidity.

The definitions of occludable angle and manifest PACG were based on definitions agreed on by the World Glaucoma Association (WGA).7,8 In this study, PACS was defined as present if either eye had the posterior trabecular meshwork not visible for 180° or more on gonioscopy.19,20PAC was present in an eye with PACS and peripheral anterior synechiae (PAS) and/or IOP ≥ 21 mm Hg (the 97.5th percentile of IOP in the HES study population is 20.3 mm Hg in the right eye and 20.8 mm Hg in the left eye), but without glaucomatous damage of the optic disc. PACG was defined as PAC with evidence of glaucomatous damage of the optic nerve.

To report the prevalence of PACG, we included both “definite” and “probable” cases as having been done previously.1,21,22 Subjects with PACG had no secondary cause of glaucoma and met the above-cited criteria. For the subjects with unilateral pseudophakia or aphakic eye, the other eye's angle would be the reference to differentiate PACG or primary open-angle glaucoma (POAG); for those with bilateral pseudophakia and/or aphakic eyes, documented records would be suggestive; otherwise, the case could be open-angle glaucoma, or underdetermined; for those with PAS but without angle closure in the rest of the angle and no history records of angle closure, we classified their status as underdetermined, not secondary angle-closure glaucoma.

Statistical Analyses

Prevalence of PACS, PAC, and PACG was calculated as the ratio of the number of individuals with PACS, PAC, and PACG to the total number of participants in whom the diagnosis could be made. Those examined at home were not included because gonioscopy was not performed on these individuals. If a person had angle closure in either eye or both eyes, the person was defined as having angle closure and categorized as PACS, PAC, or PACG accordingly. If one eye had PACG and the contralateral eye was PAC (or PACS), that person was defined as having PACG; if one eye had PAC and the contralateral eye was PACS, that person was defined as having PAC. Blindness was defined as best-corrected visual acuity < 20/400.

The prevalences of PACS, PAC, and PACG were standardized by age and sex to the national population census of China (2000). All analyses were conducted at the 0.05 significance level and used commercial software (SAS ver. 9.1.3; SAS Institute Inc., Cary, NC).

To compare with other studies using the definition developed by the International Society of Geographical and Epidemiologic Ophthalmology (ISGEO), we also presented the classification of primary angle-closure diseases with the ISGEO definition.7 Briefly, this scheme made the identification of glaucoma on three levels of evidence. The highest level of evidence requires optic disc and visual field evidence (VCDR or asymmetry ≥ 97.5th percentile and reproducible glaucomatous field defect). In the second, if the visual field test could not be performed satisfactorily, a severely damaged disc (VCDR or asymmetry ≥ 99.5th percentile) is considered compatible with glaucoma. The third level of evidence specifies that if the optic discs cannot be examined due to severe media opacity, subjects who are blind (corrected visual acuity < 20/400) and had undergone previous surgery, or have an IOP ≥ 99.5th percentile, are classified as having glaucoma.10

Results

Of 7557 eligible persons 6830 subjects (90.4%) participated in the study. However, home visits were performed on 114 of these, and the remaining analyses were on the 6716 who received complete examinations. Limbal anterior chamber depth (LACD) assessment was possible in almost all subjects. Among 413 subjects with LACD > 40% who were systematically sampled to have gonioscopy performed, 30 subjects (7.3%) had PACS and 3 subjects (0.73%) had PAC in one eye or both eyes; however, none had PACG, and 2 of the 3 subjects with PAC had an IOP > 21 mm Hg and, thus, would have had gonioscopy performed according to study protocol. Using a cutoff of 40% for LACD therefore had a specificity of 92.0% for ≥180° of angle closure on gonioscopy. Further requiring gonioscopy on those with elevated IOP meant that only one PAC in over 400 subjects was missed.

Primary Angle-Closure Glaucoma

There were 32 subjects (20 females, 12 males) with definite PACG (0.5%; 95% confidence interval [CI]: 0.3–0.6%). Eleven cases of PACG lacked sufficient optic disc information and did not have reliable visual fields. In these cases the diagnosis was based on a high IOP, with a history consistent with glaucoma along with vision loss. Measurements (mean ± SD) were as follows: age: 65.8 ± 11.7 years; mean IOP: 22.3 ± 12.0 mm Hg; and mean VCDR: 0.79 ± 0.23 (Table 1). Five cases of PACG had LACD > 40%; two of them had prior surgery (one had undergone trabeculectomy and the other iridectomy in both eyes); and three others had definite angle closure on gonioscopy, with PAS and glaucomatous optic neuropathy in one eye.

‖Used the data in the better-seeing eye; because of unreliable or missing data, only 759 were available for the Normal group, 254 for the PACG group, 63 for the PAC group, and 22 for the PACG group.

In all, 15 females and 6 males with PACG (65.6%, 21/32) were blind in at least one eye and only 2 female participants (6.25%, 2/32) were bilaterally blind. Among the 21 blind persons with PACG in this study, 13 subjects (62%) were believed to be blind from PACG, 6 subjects (28.6%) were believed to be blind from cataract, one subject (5%) had optic nerve atrophy (which may have been a result of a prior angle-closure attack), and another subject (5%) had a dense corneal opacity, which may also have been the sequelae of PACG. One case (50%) of bilateral blindness was definitely due to PACG. A reliable visual field was available in 22 subjects; the mean deviation (MD) was −8.2 ± 8.1 dB in the better seeing eyes (Table 1). In all, 21 subjects (65.6%) had been previously diagnosed with glaucoma, 9 of whom (42.9%) had undergone surgery and one of whom (4.8%) was treated with medications; the remaining 11 subjects (52.3%) had never been treated and 8 of the untreated cases were blind in at least one eye. Four of the patients with PACG (12.5%) had a family history of glaucoma.

Primary Angle Closure

There were 108 subjects with PAC; the crude prevalence was 1.6% (95% CI: 1.3–1.9): 83 were female (2.2%; 95% CI: 1.8–2.8) and 25 were male (0.9%; 95% CI: 0.5–1.1). Mean IOP was 18.4 ± 4.4 mm Hg; mean VCDR was 0.44 ± 0.12; and mean age was 61.3 ± 9.6 years (Table 1). In all, 36 (33.3%) of the 108 subjects had a presenting IOP > 21 mm Hg, 72 subjects (66.7%) had PAS, and 6 subjects (5.5%) had both. Six of the subjects who had a history of acute attack had been treated with trabeculectomy or iridectomy, one had been treated with medicine, whereas the others had no previous treatment.

Subjects with PACS and PAC were approximately 10 years older than normal people (P < 0.001), whereas subjects with PACG were approximately 5 years older than those with PACS or PAC (P < 0.001). IOP was similar in patients with PACS and that in normal persons, significantly lower than that in subjects with PAC and PACG (P < 0.001). The spherical equivalent (SE) in normal persons was similar to that in subjects with PACG (P = 0.812), but was more myopic than that in subjects with PACS and PAC (P < 0.001). Axial length and anterior chamber depth in all angle-closure diseases were smaller than measurements in normal people (P < 0.05); lens thickness was greater than that in normal people (P < 0.05), but there were no significant differences among subjects with PACS, PAC, or PACG (P > 0.05). CCT in persons with PACG was not different from that in subjects with PACS (P = 0.444) and normal persons (P = 0.101), but lower than that in persons with PAC (P = 0.012). The MD of visual field defects was −3.2 ± 3.7 in the normal group (n = 759), and −3.6 ± 4.2 for PACS (n = 254), −4.5 ± 4.2 for PAC (n = 62), and −8.2 ± 8.1 for PACG (n = 22). Visual field defects were significantly higher in the PACG group than those in the other three groups (P < 0.005); MD in PACS did not differ with that of the normal group (P = 0.08) and the PAC group as well (P = 1.66) (Table 1).

Age- and sex-adjusted prevalence rates of PACG, PAC, and PACS for 40-year-old subjects (based on the national census population for China 2000) were 0.5% (95% CI: 0.3–0.7%), 1.5% (95% CI: 1.2–1.8%), and 10.4% (95% CI: 9.6–11.2%), respectively (Table 2). There was an increase in the prevalence of all three conditions with age (Fig. 1).

The prevalence is based on the individual (either eye of the individual); the diagnosis is made when the particular characteristic is identified in either eye. The diagnosis is made according to the eye with the more severe form if the disease status is different in the two eyes. For example, when the case presented with suspect angle closure in one eye and with PAC in the other eye, a diagnosis of PAC instead of suspected angle closure is made. The prevalence rate for PACS refers to occludable angles found by gonioscopy not including PAC and PACG. PAC did not include PACG.

We have 11 cases with PAS that did not meet the gonioscopic criteria for angle closure. Among the 11 cases: 4 had a history of glaucoma surgery (3 were PACG or PAC, 1 was POAG); 2 cases had a history of cataract surgery, one of them had normal IOP, normal optic disc, and normal anterior chamber in both eyes (we believed that PAS was secondary in this case). The other case had elevated IOP and definite PAS, angle-closure glaucoma (ACG) history, and GON; thus, this patient was determined to be in the PACG group. There were 5 cases with 1 to 3 clock hours of PAS: in 2 of these cases, the fellow eye met the criteria of PACS, so we included them as PACS eyes; 3 other cases had one quadrant of angle closure but, according to the definition being used in this study, we did not include them as having PAC.

According to the definition recommended by ISGEO, 51 cases (0.76%) would be diagnosed as PACG. A total of 109 cases (1.62%) would be diagnosed as PAC and 775 cases (11.5%) would be diagnosed as PACS (Table 3). The age–sex standardized prevalences of PACS, PAC, and PACG with the ISGEO approach are summarized in Table 4.

Quigley and Broman1 estimated that by 2010 the prevalence for ACG worldwide would be 0.69%, 87% of ACG cases would be in Asia, and 47.5% of them would be in China. In the present study, we found that the prevalence of PACG was 0.5% (95% CI: 0.3–0.7%) among people 40 years of age and older in a rural Chinese population, lower than previous estimates for Chinese persons. When using the national census population to standardize to the prevalence older than 50 years of age, the estimate is 0.8% (95% CI: 0.5–1.1%) with HES experts' consensus and 1.1% with ISGEO definition similar to what has been reported in urban residents in Guangzhou (1.0%)10 and Beijing (1.3%)23 (Table 5).

*Standardized prevalence by age according to National Census Population China (2000).

†The age-specific prevalence in this study was not available; the standardized prevalence was extracted from Foster and Johnson.2

The prevalence of PACG was higher in population-based studies by the Beijing Shunyi Study group, in which the prevalence was 1.37% among people 40 years of age and older in 19894 and 1.66% in 2002.3 Another group reported the prevalence to be 1.2% in Beijing in 2005.6 However, with the exception of the Liwan Eye Study, all the above-cited studies included some of the symptomatic PAC or acute angle-closure (AAC) subjects as having PACG; therefore, the prevalence was likely inflated. The present study followed the international definition recommended by WGA,8 in which PACG was defined as angle closure combined with evidence of glaucomatous optic nerve damage or visual field loss. Using a definition similar to that used in these early reports and including those with a medical history of “AAC,” “acute angle-closure glaucoma,” or “PAC/PACG,” the prevalence would have increased to 1.3% (95% CI: 1.0–1.6%) for persons 40 years of age and older, comparable to what was reported in both the Shunyi Study and the Beijing Eye Study.3,6

The prevalence of PACG among Chinese in the present study is similar to what has been reported for Singapore Chinese and Indians, but lower than that reported in Mongolia, where the sample size was small and had a very wide 95% CI (0.1–2.2%) (Table 5).24 The rate in the present study is higher than that reported in White, Hispanic, and Black populations. The Melbourne Visual Impairment Project in Australia reported only a 0.1% prevalence of PACG diagnosed at the discretion of the ophthalmologists.28 In a Hispanic population 40 years of age or older, there was a 0.10% prevalence of PACG.29 In an African tribe, a prevalence of 0.1% was found with PACG defined as glaucomatous optic neuropathy and an occludable drainage angle.30 However, a relatively recent study from northern Italy found a 0.6% prevalence of PACG in a population 40 years of age or older,31 and the researchers required glaucomatous optic nerve damage in the definition of PACG. However, this study in a rather isolated Italian village may not be representative of the other European-derived populations.32

The prevalence of PAC was quite similar among those 50 years of age and older between the present study and the Liwan study (2.3% vs. 2.4%). However, the prevalence of PACS (14.9%) was higher than that reported in the Liwan study (10.2%) among persons 50 years of age and older,10 but we defined PACS when the 180° angle of trabecular meshwork was not visible, whereas the Liwan study defined PACS with 270°. When we required 270°, our prevalence of PACS was 10.8%, similar to that found in Liwan, but higher than that reported in Mongolians (6.3%) and Singapore Chinese (6.4%).2 All reported prevalences of PACS among Chinese are much higher than those reported in Whites (0.8%) and in African Americans (0.6%).33

Age is known to be strongly associated with PACS, PAC, and PACG.6,10,17,24,26,34 Among those with an age range from 30 to 39 years, only two (0.2%) had PACG and the prevalence was 10-fold higher among those 70 years of age or older (Fig. 1). As in previous reports, females accounted for two thirds of all three conditions.1,10,17,24

Two thirds of patients with PACG were blind in at least one eye, a finding similar to that seen in Mongolia (70%),24 and slightly higher than that reported in Singapore Chinese (50%)17 and urban residents reported in the Liwan study (42.9%).10 In India, the reported ratio of blindness in at least one eye was 33.3% in one study35 and 14.7% in another, and it is possible that the natural history of PACG varies by region.26 Alternatively, glaucoma blindness may in part be related to care provided, and the higher rates in Mongolia and rural China may reflect the lower access to eye care in these regions.

Further supporting this argument is the fact that not all blindness in PACG patients was due to glaucoma. Among the 21 blind persons with PACG in this study, 13 subjects (62%) were believed to be blind from PACG, 6 subjects (28.6%) were believed to be blind from cataract, one subject (5%) had optic nerve atrophy (which may have been a result of a prior angle-closure attack), and another subject (5%) had a dense corneal opacity, which may also have been the sequelae of PACG. However, the ratio of blindness was much higher in PACG than that in POAG, where only 3 of 67 persons were blind in one eye (4.5%) and none was bilaterally blind observed in this study (data not shown).36

Based on the population data provided by the World Health Organization for China for 2010,37 we estimate that the number of persons identified as being PACS, PAC, and PACG were 68.9 million, 10.5 million, and 3.2 million, respectively. PACG was the cause of blindness in at least one eye for 1.3 million persons. These numbers will increase by 50% by 2020 due to the aging of the population to 92.7 million with PACS, 14.4 million with PAC, and 4.4 million with PACG. It is projected that 1.8 million will be blind in at least one eye from PACG. Angle-closure disease is rarely diagnosed at present, with over 90% of the cases with PAC and over half of the persons with PACG being undiagnosed. Given the rapid aging of the population and the projected increase in blindness rates from PACG, greater efforts need to be made to provide eye care to rural Chinese populations.

There are numerous studies reported that subjects with PACG, PAC, or PACS have shorter axial length, shallower anterior chamber depth, and thicker lens.38–42 The same was found in this study, although we did not observe that the persons with PACG or PAC had shallower anterior chamber or thicker lens than those with PACS, which is believed to be at the early process in development of angle closure. Two Indian population studies also reported similar findings,42,43 indicating that factors other than the increasing thickness of lens with age may play an important role in the development of angle closure.

It has been reported that PACG happens more often in hyperopic eyes,6,26,35,44 although in our study, the SE in PACG eyes was not very different from that of normal eyes but lower than that of eyes with PAC and PACS. The small sample of PACG may account for the lack of a significant difference. An alternative explanation may be that there was an obvious myopic shift after 65 years of age in Chinese people.14 Interestingly, CCT in persons with PACG was lower than that in persons with PAC, but showed no difference with that in PACS and normal persons. The requirement of elevated IOP for PAC diagnosis might have resulted in persons with thicker cornea having more chance to be identified as PAC.

Strengths of this study include a large sample size and high response rate. However, there are some limitations. First, we did not perform gonioscopy on all subjects but only did so on those with LACD ≤ 40% of corneal thickness or other signs of glaucoma. Since we performed gonioscopy on all subjects with suspected glaucoma, it is likely that none of the PACG cases was missed using this approach. In fact, in the systematic sample of persons with LACD > 40% on whom gonioscopy was performed, none had PACG. However, we did find that LACD missed some who met our gonioscopic definition of angle closure and, thus, the prevalence of PACS and PAC is likely slightly higher than that reported here, although for PAC we identified only one case in over 400 randomly sampled who did not meet study requirements for gonioscopy. The overall prevalence of PACS is therefore likely similar to what is reported. Second, we defined PACS groups as those with either eye having 180° of angle in which the pigmented posterior trabecular meshwork could not be seen. This approach is more likely to categorize persons who have POAG and narrow angles as having PACG than the approach used as those having 270° of angle in which the pigmented posterior trabecular meshwork could not be seen. However, only one person (0.015%) was diagnosed with PACG, but having no PAS. Finally, the methodology used to define glaucoma in this study—requiring consensus initially among one set of ophthalmologists and then requiring a second pair of ophthalmologists to agree with the initial grading—led to a reduction in the numbers determined to have definite or probable glaucoma, and may have resulted in an underestimate of the prevalence of PACG.

For comparison with other studies using the ISGEO approach, we have also presented the results using the ISGEO definition. Four cases of PACG identified by the HES expert group did not meet the ISGEO definition for glaucoma because of cup/disc ratio not greater than 0.7; and 23 cases that met the ISGEO definition of PACG were not found to have glaucoma using the HES consensus process. Although the cup/disc ratio was large in these cases and/or the visual field defects were reproduced, we did not believe that the findings were consistent with a diagnosis of glaucoma. These subjects were categorized as having either PACS or PAC. The HES experts were more conservative than the ISGEO algorithm in part because photographic images can vary in quality as can visual fields. Relying solely on nonphotographic grading at the slit lamp by a single observer seems to us to be prone to misdiagnosis. Our planned follow-up study will be valuable in determining what ultimately happened in these controversial cases.

In summary, this study provided further information about the prevalence and characteristics of PACS, PAC, and PACG in a rural Chinese population, in which the rate is similar to that reported previously in urban Chinese residents. However, two thirds of the subjects with PACG were suffering from blindness in at least one eye. A strategy to detect and treat the angle-closure diseases should be taken to reduce the visual burden of angle-closure glaucoma in China.

Footnotes

Supported in part by National Basic Research Program of China (Program 973) Grant 2007CB512201 from the Ministry of Science and Technology of the People's Republic of China; Program of Health Policy for Blindness Prevention from the Ministry of Health of the People's Republic of China; the Key Technologies R&D Program; the Bureau of Science and Technology of Handan City, Hebei Province, China Grant 2006-10903; Beijing Tongren Hospital; and the Key Discipline Fund of the Bureau of Health, Handan City, Hebei Province, China.

Vijaya
L
George
R
Arvind
H
. Prevalence of primary angle-closure disease in an urban south Indian population and comparison with a rural population. The Chennai Glaucoma Study. Ophthalmology. 2008;115:655–660.[CrossRef][PubMed]

WHO Population Division. World population prospects: the 2006 revision of population database: population by five-year age group and sex in China. Available at http://esa.un.org/unpp/p2k0data.asp
. Accessed at December 17, 2010.

38.

Tomlinson
A
. Age in angle-closure glaucoma and the normal: a study in profile photography. Br J Physiol Optics. 1974;29:57–63.

The prevalence is based on the individual (either eye of the individual); the diagnosis is made when the particular characteristic is identified in either eye. The diagnosis is made according to the eye with the more severe form if the disease status is different in the two eyes. For example, when the case presented with suspect angle closure in one eye and with PAC in the other eye, a diagnosis of PAC instead of suspected angle closure is made. The prevalence rate for PACS refers to occludable angles found by gonioscopy not including PAC and PACG. PAC did not include PACG.